At the Seoul Motor Show today, Hyundai Motor Company unveiled the world's first hybrid electric vehicle to be powered by a Liquefied Petroleum Injected (LPI) engine. The Elantra LPI Hybrid Electric Vehicle (HEV) will also be the world’s first hybrid vehicle to adopt advanced Lithium Ion Polymer batteries. Hyundai has leveraged its world leadership in LPG fuelled vehicles to develop a hybrid that will be very economical to operate.
The technology and all key components in the Elantra LPI HEV have been developed by Hyundai and its local partners including the motor, battery and low DC/DC converter.
A unique instrument cluster was developed for the Elantra LPI HEV. Visibility is improved by using a semi-supervision type panel and a negative Liquid Crystal Display (LCD) for the odometer / trip metre. Visibility is enhanced by a radiant type LED backlight and uniform intensity of illumination. The cluster is integrated into the Control Area Network (CAN).
Hybrid Blue Drive Architecture
The Elantra LPI HEV is based on a flywheel mounted motor-generator type parallel hybrid system independently developed at Hyundai’s Hybrid Vehicle Development Centre in Namyang, Korea.
Powered by an LPI ‘Gamma’ engine displacing 1.6 litres, a 15 kW (105 Nm) electric motor and a Continuously Variable Transmission (CVT), the Elantra LPI HEV is a mild–type hybrid capable with a fuel economy rating of 5.8 litres / 100 km (or petrol equivalent of 4.7 litres / 100 km): This represents a 41.4 percent improvement over a conventional 1.6 litre Elantra with automatic transmission.
In Australia, a typical petrol automatic sedan achieves a fuel consumption^ of around 7.8 litres / 100 km. At 110.9 cents per litre+ for unleaded petrol in Sydney, it would cost a motorist $25.95 in unleaded petrol to drive their petrol sedan over 300 km each week (or $4,048.20 over 3 years).
Hypothetically, given a price of 54.4 cents per litre+ for LPG in Sydney, it would cost a motorist $9.47 of LPG to operate an Elantra LPI Hybrid car over 300 km each week (or $1,477.32 over 3 years).
A simple comparison between a typical petrol automatic sedan sold locally and the Elantra LPI Hybrid Electric Vehicle, shows that the Hyundai Elantra LPI HEV would save driver’s approximately $2,570 in fuel costs over 3 years.
For improved thermal efficiency, the Atkinson cycle* is employed and the compression ratio has been increased from 10.5 to 12.0. To increase mechanical efficiency, the valve spring load and piston ring tension were reduced. Further reductions in friction were achieved by coating the tappets with a Diamond-Like Carbon (DLC) coating and adding a Molybdenum Disulfide (MoS2) coating to the piston skirts. Also, Continuously Variable Valve Timing (CVVT) was applied on the intake camshaft and an Electronic Throttle Control was adopted.
The CVT is equipped with a new Van Doorne type metal transmission belt and in the interest of better fuel economy; a wet type multi-disc has been installed as a starting device instead of a torque converter. A chain driven external gear type oil pump and torsional damper are installed on the front side of the CVT. Also, special step cut seals are applied to minimise leakage. On starting the clutch, a direct solenoid is used for precise control and a separate / variable cooling system is applied. As a result of these improvements, the transmission efficiency of the CVT is higher than its competitors. In addition, a hydraulic ‘limp-home’ mode is available in case of transmission control unit (TCU) malfunction.
The electric motor in the hybrid powertrain is a pancake type Interior Permanent Magnet Synchronous Motor (IPMSM) installed between the engine and the CVT. The IPMSM includes a revolver type position sensor which sends rotor position data to the MCU. The peak power and torque is rated 15 kW (105 Nm) and 15.7 kW (125 Nm), respectively. The peak efficiency of the motor itself is over 95 percent. The magnet shape and arrangement of the motor ("gull-wing" type) is optimized for better performance. Also, a split type winding core has been applied on the stator. The MCU and battery system share an integrated forced air cooling system. The electric motor is air-cooled.
The Elantra LPI HEV will be the first car in the world to use Lithium Ion Polymer rechargeable batteries, which will be supplied solely by LG Chem, a global leader in batteries.
Lithium Ion Polymer batteries have significant advantages over Lithium Ion batteries including higher energy density, lower manufacturing costs, being more robust to physical damage and they can also take more charge–discharge cycles before storage capacity begins to degrade. The Lithium Ion Polymer battery has passed Hyundai's 300,000km durability test and has been thoroughly tested for overcharging and collision safety.
The battery operates at a nominal voltage of 180 V and has a capacity of 5.3 Ah. The battery pack is packaged together as a part of the Integrated Power Module along with the Battery Management System, Motor Control Unit, DC/DC converter and cooling fan which controls the battery temperature within an allowable range to prevent melting or explosion. The role of the BMS is to monitor the status of the entire system and control the temperature accordingly.
Low DC / DC Converter
Unlike a conventional vehicle, the Elantra LPI HEV does not have an alternator. In its place, there is a DC / DC converter which in the interest of improved fuel economy replaces the conventional alternator to supply energy for auxiliary power needs.
The Hybrid Electric Control Unit (HCU) is a supervisory controller. Using information from the vehicle, driver, engine, power electronic components and battery, it determines the operation of the engine, transmission, motor and sends out control signals as a command / request to controllers.
In a HEV in which the traction motor is directly attached to the engine and transmission through a clutch instead of a torque converter, there is a problem of backward slip on slanted roads at the moment of engine restart after idle stop. To prevent slippage, a creep aid system has been devised into the brake system. The function of the anti-slip system is to briefly maintain brake oil pressure just after the driver has released the foot brake to make enough creep torque at engine restart. An inclinometer has been installed as part of the system to measure the gradient of the road. The HCU controls the system with input from the inclinometer to avoid take-off delay and surge on a level road. To measure the gradient of a road with the inclinometer, complex algorithms are implemented to avoid detection error caused by real road conditions.
The Elantra LPI HEV emits just 102 g / km of CO2 and 90 percent fewer emissions than an equivalent standard petrol–powered Elantra to qualify as a Super Ultra Low Emission Vehicle (SULEV). Liquefied Petroleum Gas (LPG), often referred to as auto gas, is a low carbon emitting hydrocarbon fuel which burns more cleanly than petrol or Diesel and is especially free of the particulates associated with the latter.
Retail pricing will be announced on July 1st when the car arrives in South Korean domestic showrooms. The Elantra LPI HEV will entail a small cost premium compared to a conventional model due to the extra hardware (Lithium Ion Polymer battery, DC motor and electrical control system) and associated development costs.
However, in comparing operating costs among different HEV models currently available in the global marketplace, the Elantra LPI HEV promises to be the most economical of all to run as LPG fuel is approximately half the price of petrol. The Elantra LPI HEV promises to be as much as 40 percent cheaper to operate than other competitor models in the marketplace and 50 percent less than a conventional Elantra model powered by a petrol–only engine.
Because some 15 percent of passenger car and 100 percent of taxi registrations in South Korea are LPG fuelled, the Elantra LPI HEV is certain to be a sales hit. Moreover, the Elantra has been a perennial top seller in Korea ranking among the top three on the sales charts since its introduction.
Hybrid Development Background
Hyundai developed its very first hybrid electric vehicle in 1995 when it unveiled the Future Green Vehicle at the Seoul Motor Show. In 1999, it showed an Elantra HEV and in 2000, an Accent HEV, both of which featured hard–type parallel electric drive systems and integrated Starter Generator technology. However, these research development vehicles did not go into mass production.
In 2004, the company delivered 50 Getz petrol–electric hybrid vehicles (B–segment vehicles badged as Hyundai Click in the Korean domestic market) to Korean government agencies as part of a fleet demonstration project. These were mild–type hybrid systems using 12 kW motors and nickel metal hydride batteries. The hybrid technology development program continued to expand and in 2005, Hyundai and its affiliate Kia Motors Corporation delivered 350 more units to the demonstration fleet, 730 more units in 2006 and 1,682 more units in 2007, including Accent HEVs.
For a country which must import every drop of oil, the arrival of the Elantra LPI HEV is being hailed as a small but important step forward in reducing national energy consumption and promoting diversified energy usage.
Initial sales of the Elantra LPI HEV are to be restricted to the Korean domestic market. However, the LPI Hybrid could be exported to markets which are served by an excellent LPG distribution infrastructure, although it is too early to confirm anything more.
^Source: ADR 81/02 static laboratory combined average city & highway cycle test. Fuel consumption will vary depending on a combination of driving habits and the condition of the vehicle.
+Source: Information sourced from MotorMouth
*Note: Compared to the more prevalent Otto Cycle four-stroke combustion engine, the Atkinson Cycle has a power stroke which is longer than the compression stroke and is widely adopted by designers of Hybrid powertrains due to the increase in fuel economy it provides.
Internal combustion engines can be divided into several categories according to the combustion principles: Otto Cycle, Miller cycle, Lenoir cycle, Atkinson cycle, Brayton / Joule cycle, Diesel cycle and Homogeneous Charge Compression Ignition.
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